Conventional total internal reflection (TIR) based displays include a transparent high refractive index front sheet in contact with a lower refractive index fluid. The front sheet and fluid have different refractive indices that may be characterized by a critical angle. The front sheet may be designed such that when light rays are incident upon the interface of the high refractive index front sheet and low refractive index fluid at angles less than the critical angle, they may be transmitted through the interface. When light rays are incident upon the interface at angles greater than the critical angle they may undergo TIR at the interface. A small critical angle is preferred at the TIR interface since this may afford a large range of angles over which TIR may occur. Fresnel reflections may also be present.
Conventional TIR-based reflective image displays further include electrophoretically mobile, light absorbing particles. When particles are moved by a voltage bias source to the surface of the front sheet they may enter the evanescent wave region and frustrate TIR. Incident light may be absorbed to create a dark state observed by the viewer. When the particles are moved out of the evanescent wave region, light may be reflected by TIR. This may create a white state that may be observed by the viewer. An array of pixelated electrodes may be used to drive the particles into and out of the evanescent wave region to form combinations of white and dark states. This may be used to create images to convey information to the viewer.
A high refractive index front sheet in conventional TIR-based displays further comprises an array of regularly spaced structures on the inward side facing the low refractive index medium and electrophoretically mobile particles. The array of regularly spaced structures may allow for TIR at their surface when incident light is greater than the critical angle. Light may be reflected in a semi-retro-reflective manner (semi-retro-reflective light may be described as light emitted from a display surface that follows a path less than about 30° from the typical incident ray path). In some applications it may be preferred that light is reflected in a more diffuse manner.